Cold cathode tube



July 22, 1952 J. E. M LINDEN, JR

COLD CATHODE TUBE Fild Nov. 10, 1947 INVENTOR. Jfl/77E5. E. 7775 LINDEN, JR.

BY V flfi'OK/VEY- Patented July 22, 1952 'COLD CATHODE TUBE James E. McLinden, Jr., Rego' Park,- N. Y., as signor to Bendix' Aviation Corporation, Teterboro, N. .L, a corporation of Delaware Application November 10, 1947, Serial No. 785,051-

13 Claims.

This invention relates to cold cathode tubes in which materials of a lowwork function are used in forming the cathode.

An object of my present invention is to provide a tube having a cathode of- .low work function which will furinsh high peak-currents of short duration at moderate repetition frequencies from alow frequency, low tension source of supply suitable for high frequency ignition systems, switching circuits, exciters, and puls'ers.

Another object of my invention is to provide a tube having a cathode ofa low work function material, with a sputtering inhibitor'by which arcing. and shorts occuring in the tube are materially reduced.

A further object of this invention is to provide a tube having a low work function material as a cathode with increased spacings between the elements thereof to prevent shorts and premature arcing. due to sputtered'cathode material.

Still another object of the invention is to provide a tube of the character indicated in which the dissipation of the heat generated by the cathode is greatly improved, reducing thereby the evaporation of the active cathode material.

Still a further object of my invention is to pro.- vide a highly improved cold cathode tube of the character indicated which shall consist of few and. simple parts readily assembled in mass pro-' duction, the resulting assembly being mechanicallyf rigid and free of vibrations; which shall be "positive in its action and have a comparatively-long-life, and which shall have a large variety of applications and yet be practical and-efficient toa high degree in use.

Other objects of my invention will in part be obvious, and .in part hereinafter pointed out.

The improved cold cathode tube provided by me comprises a cathode of a-low work function, a control grid and an anode hermetically sealed in an. envelope filled'with helium. The cathode of the-present invention is made by compressing powdered cesium chloride and aluminum with nickel filings into a pill of desired form and mounting the same in a cathode cup. The cathode cup engages the glass envelope enclosing the tube elements to facilitate dissipation of the heat generated in the cathode pill.

Metallic cesium is the active part of the cathode thus formed. Since metallic cesium has an ex tremely low work function which permits electrons to be emitted at low temperatures, a cesium compound is used to inhibit the vaporization of the cesiume While I have indicated cesium chloride as the preferred compound in the mantl facture of thecathodes, it will be readily appreciated that other low work function materials aluminum powder indicated as being preferred.

The control grid of my tube is made of carbon preferably in the form of graphite, cylindrical in shape and encompassing a tungsten anode. The

grid is made of carbon so that any sputtered cesium will not readily adhere thereto.

Upon application of a proper voltage to the control grid, an initial glow discharge will take place between the grid and the normally grounded cathode. When the current reaches a suflicient density at the surface of the cold cathode, a cathode spot is formed. The action of the cathode spot permits the cesium chloride to decompose, aluminum taking the place of the cesium to form aluminum chloride. layer of cesium is thus formed on the surface of the cathode pill which will cause an are discharge between the cathode and the anode.

In an arc discharge of the character described,

the sputtering of the cesium has been a problem in previous tubes of this character. The carbon grid provided-does-reduce the problem of sput-' tered cesium in that cesium'will not readily ad here thereto. There is therefore no emission from the grid to'the anode due to the sputtered cesiur'n'to cause premature arcing between these elements. By increasing the spacings of the tube elements I also reduce the inherent tendencies of premature arcings.

Nickel filings are added to the cathode ,pill to reduce the sputtering of the active materiaL.

The nickel filings in the pill reduce the cathode surface-resistance and cause the arcs to strike the exposed nickel filing particles rather than the activematerial itself. The large bursts of current will not erupt the active material, the are taking place between the nickel filings and the anode. I

By providing an external cathode cap for my tube, I increase the rate of heat dissipation of 1 the heat developed by the cathode pm. The evaporation of the cesium is thus materially reduced, reducing the inherent sputtering and increasing thereby the active life of the tube. -A-

further advantage gained by the use of my external cathode cap is the prevention of cesium deposits onthe cathode support. Arcs to the anode from the cathode support are thus prevented, as was heretofore prevalent.

A thin Accordingly, in the accompanying drawings I have shown one of the various possible illustrative embodiments of my invention, of which Fig. 1 is a vertical cross-sectional view with portions thereof in elevation, of a cold cathode tube embodying my invention and taken approximately along the line |l of Fig. 2,

Fig. 2 is a cross-section view taken'along the line 2-2 of Fig. 1, while i Fig. 3 is a cross-sectional view taken along line 33 of Fig. 1.

Referring now to the drawings, the numeral I designates a cold cathode tube embodying my invention. The tube comprises a glass sleeve H having fixed therein and made integral with-the bottom edge thereof, a second glass sleeve I2.:e.X- tending upwardly within the tube II and terminating in a three-sided glass press I3 (Fig. 3).

Supported on, and fixed to the upper face of the I glass press is a ceramic insulator l4 formed with coeggtensive and concentric openings l5, l8 and I] ofdifferent diameters/openings l5 and I6 forming an annular shoulder l8 for the. purposes,

Cut into the top surface of portion 2l'is an annular. groove 25. Supported in said groove'in an in erted positionand facing inwardlyof the envelope is a cathode cup 26 preferably made of.

nickel, Substantially the entire outer surfaceof the cathode cup engages a cathode cup 21, preferably of kovar;- the loweredge of the cap being sealed to the glass sleeve I! to form a hermetically sealedtube The sealed tube is filledpwith an inert gas, preferably helium.

Fixed withinthecathode cup 2 5 is a cathode o mi g the actual cathode for-the tube l0.

. powde a d ni l-fili e i o e d siredforrn; The; pill is held with-inthe cup by a wire; mesh screen 3|, preferably made of nickel.

A, carbon grid 32, cylindrical: in form is fixed within the-openings I5 and {6 of the ceramic insulator. The grid 32 is formed with an annularshoulder 33 on its exterior and a tapered bore 34 in its interior. The grid shoulder 33 abuts the shoulder 18 of the insulator to space the grid properly within the insulator so that the gridextends; slightly above the upper end of opening Hi. The taperedbore 34 of the grid forms a partial enclosure for a rod-like tungsten anode 35-. A glass bead 36 ;aboutthe lower end of the anode serves to reduce thepossibility of shorts or-arcing, v

Electrical connections are provided for the grid 32 and the anode; 35 through the glass press I3 by two lead-in wires 38 and 39. .The grid 32 is connected to the lead-in wire 38 by a contactor 40 fixed into the glass press and fitting within an opening 4i formed in the insulator M The cathode 30 of the tube is connected byway of the cup and cap into the electrical circuit.

With;proper voltage applied ;to thegrid 32;, a glow discharge will take placebetween .the grid and the cathode 3-0,: The decomposition of the cesium chloride of the cathode-will form acathration of the-active material is reduced adding ade; by compressing cesium chloride, 7

ode spot on the pill which will emit electrons to form a low resistance path from the cathode to the anode 35. An arc discharge will then take place between anode and cathode, the arc striking the nickel filings of the cathode pill rather than the active material of the pill. It was found that the nickel screen 3| retaining the cathode pill within thecup 26 did not prevent the pitting of the pill when the arc was struck. The nickel filings however compressed in with the cesium chloride and aluminum did prevent the objectionable pitting heretofore found in available cold cathode tubes.

The heat developed'in the cathode is quickly dissipated by the external cathode cap. Evapomaterially to the life of the tube.

It should be noted that'sputtering of the active material is inherent in tubes of this character.

The arcing and shorts resulting from sputtered material has been materially reduced by the use of the nickel filings in the pill and by increasing the spacings of the tube elements. I

In the construction described, the ceramic insulator i i has been provided with a series of slots I9 registering with the opening El between the cathode and the grid. From'Fig. .2 it will be apparent that only a knife edge of the pillars 29 lies in the path between the cathode and; The-minute particles of activ material.

anode. will therefore pass out of the slots l9 into the space between the insulator and the envelope.

The cesium-particles will adhere to the exterior of the insulator and to the faces of the wedges 28,

rather than to the knife edges. .With thesputtered material. deposited at considerable distance'from'the tube elements, the voltages appliedto the grid or anode will-be insuflicient to bridge the extra distance to cause the shorts and arcing heretofore had in tubes of thistype.

A further advantage in the construction describedis the solid support provided for the..insulator M by the three-way glass press 13, .The grid.3.2 nested within the insulator and the extremely short anode 35 fixed into the press '3 prevents fracture and displacement of these elementsbyany vibrations acting upon the tube. The cathode 383 is also rigidly mounted within the tubelenvelope and is supported by the ccramic insulator.-

There is thus provided a highly improved cold cathode tube having a long life in which sputtering ofthe active materials has been materially reduced, in which shorts and premature arcing is virtually eliminated, in which evaporation of the active material has been reduced by increas-- ing the heat dissipationof the tube and in which the tube elements are mechanically rigid.

As various possible embodiments may be made of the above invention, and as various changes might be made in the embodiment above set forth, it'is to be understood that all matter here in set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

Having thus described my'invention, I claim as new and desire to secure by Letters Patent:

1. A gaseous discharge tube comprising an envelope, a cylindrical'insulator fixed'withinsaid envelope, a cylindrical control grid of carbon nested within said insulator, an inverted cup supported by said insulator and spaced from said grid, a plurality of openings in said insulator between said cupand said grid, a pill containing a material of low work function in said cup form-- ing the cathode of the tube, nickel particles in said pill, a wire mesh screen to retain said pill in said cup, a tungsten anode fixed within said insulator, and an inert gas filling said envelope.

2. A gaseous discharge tube comprising an envelope, a cylindrical insulator within said envelope, a cylindrical carbon grid nested within said insulator, an anode encompassed by said grid and fixed within said insulator, a cup supported by said insulator and spaced from said grid and anode, a pill containing a material of low work function within said cup and forming the cathode of the tube, nickel particles in said pill, and an inert gas within said envelope.

3. A gaseous discharge tube comprising an envelope, a cylindrical insulator mounted within said envelope, 2. carbon grid fixed to said insulator, a cup supported by said insulator and spaced from, and facing said grid, a pill containing a material of low work function within said cup, nickel particles within said pill, an anode fixed within said insulator in proximity to said grid, and an inert gas filling said envelope.

4. A gaseous discharge tube comprising an envelope, a cylindrical insulator fixed within said envelope, a carbon grid fixed to said insulator, a cup supported by said insulator and engaging said envelope and spaced from said grid, a plurality of vents in said insulator between said cup and said grid, a pill containing a material of low work function within said cup, and an anode in proximity to said grid fixed within said insulator.

5. A gaseous discharge tube comprising an envelope, a cylindrical insulator therein having three coextensive openings of different diameters, a cylindrical grid nested within the first two of the openings of said insulator, a cup supported by said insulator and closing the third of said openings, a plurality of transverse slots in said insulator between said cup and said grid registering with the third of said openings in said insulator, a pill containing a material of low work function in said cup forming the cathode of the tube, an anode fixed within the first of said openings in said insulator and encompassed by said grid, and an inert gas in said envelope.

6. A gaseous discharge tube comprising an envelope, a cylindrical insulator fixed within said envelope and having at least two coextensive openings of different diameters, a grid fixed in the smaller of said openings and extending into the larger of said openings, a cup supported by said insulator and closing the larger of said openings, a plurality of transverse vents in said insulator between said cup and said grid registering with the larger of said openings in said insulator, a pill containing a material of low work function forming the cathode of the tube, an anode within the smaller opening of said insulator, and an inert gas filling said envelope.

7. A gaseous discharge tube comprising an envelope, a cylindrical insulator fixed within said envelope and having at least two coextensive openings of different diameters, a cylindrical carbon grid fixed in the smaller of said openings and extending into the larger of said openings, a cup supported by said insulator and closing the larger of said openings, a plurality of transverse vents in said insulator between said cup and said grid registering with the larger of said openings in said insulator, a pill containing a material of low work function forming the oathode of the tube, nickel particles in said pill, an anode of tungsten within the smaller opening of said insulator, and an inert gas filling said envelope.

8. A gaseous discharge tube comprising an insulator fixed within the tube envelope and having at least two coextensive bores therein of different diameters, a cathode holder supported on said insulator and closing the end of the larger bore therein, a gridfixed within the smaller of said bores, a plurality of transverse vents in said insulator registering with the larger bore, and an anode in proximity to said grid and within the smaller bore of said insulator.

9. A gaseous discharge tube comprising an in sulator fixed within the tube envelope and having at least two coextensive bores of different diameters, a cathode holder supported on said insulator and closing the end of the larger bore, an annular grid fixed within the smaller of said bores, a plurality of transverse vents in said insulator registering with the larger bore, and an anode fixed concentrically with said grid within said smaller bore.

10. A discharge tube including an envelope, insulator means fixed within said envelope, a control grid and an anode supported by said insulator means, and a cathode of low work function having a cup supported by said insulator means and engaging a substantial area of said envelopes to facilitate dissipation of heat generated in the cathode.

11. A discharge tube including an envelope, a cathode of low work function having a cup mounted within said envelope and having an open end facing inwardly of the envelope and substantially the entire outer surface of the cup engaging the walls of said envelope to facilitate dissipation of heat generated in the cathode.

12. In a discharge tube, a cathode containing a compound including an element of low work function, a substance to displace the element of low work function from said compound during discharge, and free nickel particles to provide points at which the arc of the discharge occurs.

13. In a discharge tube, a cathode in pill form containing a cesium compound, powdered aluminum for reacting chemically with said compound during discharge and displacing the cesium therefrom, and nickel filings to provide points at which the arc of the discharge occurs.

JAMES E. MCLINDEN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,347 Gross May 4, 1937 2,185.189 Germeshausen Jan. 2, 1940 2,201,167 Germeshausen May 21, 1940 2,397,764 Stubbs Apr. 2, 1946 2,433,809 Clapp Dec. 30, 1947 

